Polo-like kinases (PLKs) are serine/threonine kinases that play important roles in regulating processes in the cell cycle. There are four PLKs disclosed in the state of the art, i.e. PLK-1, PLK-2, PLK-3. and PLK-4. PLKs play a role in the regulation of the eukaryotic cell cycle (e.g. regulation of the mitotic machinery in mammalian cells). Especially for PLK-1 a central role with respect to the regulation of mitosis is shown (Glover et al. 1998, Genes Dev. 12:3777-87; Qian et al. 2001, Mol Biol Cell. 12:1791-9). Overexpression of PLK-1 seems to be strongly associated with neoplastic cells including cancers (WO 2004/014899). Overexpression of PLK1 has been documented for various tumor types such as non-small cell lung cancer, squamous cell carcinomas, breast, ovary or papillary carcinomas as well as colorectal cancers (Wolf et al. 1997, Oncogene 14, pages 543-549; Knecht et al. 1999, Cancer Res. 59, pages 2794-2797; Wolf et al. 2000, Pathol Res Pract. 196, pages 753-759; Weichert et al. 2004, Br. J. Cancer 90, pages 815-821; Ito et al. 2004, Br. J. Cancer 90, pages 414-418; Takahashi et al. 2003, Cancer Sci. 94, pages 148-152).
It is the purpose of the present invention to provide compounds for the treatment of various cancer diseases.